It is well known that nuclear magnetic resonance (NMR) spectroscopy provides extremely highly detailed information on molecular structure. NMR is also quantitative because the detected signal is linearly proportional to the absolute number of active nuclei in the detected sample volume. Thus, relative numbers of hydrogen, carbon or other atoms in a molecule can be directly measured, the relative number of different molecular species in a mixture can be computed, and by using an internal standard (or even an external standard), the absolute concentration of species can be calculated.
However, when measuring the components of complex mixtures, overlapping resonances often result, which thus compromises the ability to measure concentrations quantitatively. Even small molecules often give rise to 20 or more spectral lines in the 1H NMR spectrum, leading to severe overlap for many complex mixtures. For example in the 1H NMR spectrum of human urine, over 1000 spectral lines can be at least partially resolved, corresponding to upwards of 100 compounds (See: J. C. Lindon, E. Holmes, and J. K. Nicholson, Prog. NMR Spec. 39, 1 (2001)).
The metabolomics approach, combining high-resolution NMR with multivariate statistical analysis, has been shown to be very powerful for distinguishing biofluid sample subpopulations based on subtle differences in the their spectra.1,2 This approach can be widely applied to many types of samples, including urine, body fluids, and tissues. NMR based approaches are attractive because they can look at essentially all of the components of a mixture simultaneously, and thus avoid the sometimes difficult process of sample fractionation. These methods can also be rapid and quantitative.
The present invention is intended to address one or more of the problems discussed above.